1. Field of the Invention
This invention relates generally to handknobs for hydraulic valves, and more particularly to a calibrated handknob having a zero reset feature.
2. Description of the Prior Art
Calibrated handknobs for hydraulic valves are not uncommon. They come in many forms and most are effective in indicating how many turns and fractions of a turn a valve is open. Typically, as the valve is opened by turning the knob, the knob rises with the valve stem and as the knob rises, the knob skirt uncovers calibration marks on a stationary band. An example of this type of calibrated knob is found on the micrometer used by the machinery trades.
Another popular style of calibrated handknob employs a rising stem and non-rising knob. In this style turns are indicated on a read-out column that extends past the outer end of the operating knob, and fractions of a turn are generally indicated by radially spaced lines on the knob skirt which relate to a fixed indicator on the valve body or a stationary band. An enhancement of this style is the use of differential threads to multiply the read-out column movement which make it easier to read. This is an effective modification, but it entails additional expense.
In addition to the foregoing types, there are other calibrated handknobs, but they are apt to be more complex and costly to build. In any event, all of the available designs lack one or more of the following desirable features:
1. Disassembly and reassembly in the field without special tools.
2. Detented locked and unlocked positions (usually a screw in the turning handknob or a nut on a stationary threaded band are used to lock the adjustment).
3. An inexpensive, elastomeric means for protecting the assembly from a dirty environment.
4. Knob retention without the use of threaded fasteners. Retention is important to assure that the knob is not inadvertently pulled off the assembly during use.
5. A means for adjusting the zero position for most convenient viewing.
6. A simple, inexpensive design consisting of few parts that are made by low cost production processes.
It is therefore an object of this invention to provide a calibrated handknob which will incorporate all of the foregoing desirable features